, which establishes tailored abstrac-
tion levels on demand, which may be refined by adding new
letters in the course of the systems evolution. This way
ACQC does not only allow us to reveal serious bugs sim-
ply by inspecting difference views of the (tailored) models,
but also to visually follow and control the effects of (in-
tended) changes, which complements our model-checking-
based quality control.